1. Field of the Invention
The present invention relates generally to devices for measuring the force exerted by the drawbar assembly of the spindle of a CNC machine or other similar machine that uses a drawbar for retaining a tooling arbor.
2. Description of the Related Art
Spindles on CNC machines are commonly used for manufacturing gear boxes, or a metal work piece. Such machines typically use a specific type of spindle that includes a drawbar assembly and a coupler which securely holds the tool holder. Each tool holder includes a conical-shaped body which is placed inside a complementary-shaped receiving space formed in the spindle assembly. Attached to the tip of the tool holder is a pull stud which engages a complementary-shaped slot formed on a coupler located inside the receiving space assembly.
Another type of spindle used with CNC machines uses a hollow-shank, taper anchor (hereinafter called a HSK arbor) which interfaces with the drawbar mechanism used with the HSK spindle. A HSK spindle drawbar includes a set of fingers which are forced outward by the drawbar mechanism to engage the inside rim formed on the arbor. The drawbar mechanism is then pulled inward to retain the HSK arbor within the spindle.
Various claims are made as to the benefits of each type of arbor. Generally, the consensus among machine operators is that HSK arbors and spindles are superior for high-speed machining (spindle rotations of 15,000 to 50,000 RPM) while long taper arbors and spindles are superior for low speed machinery (below 10,000 RPM).
It is an object of the present invention to provide a tension testing kit for measuring the holding force on an HSK arbor and spindle.
The testing kit includes a force exerting means similar to the structures disclosed in Applicant""s prior patent application, which is incorporated herein. The kit also includes a guide piece, a grip-housing, and a transfer rod. During assembly, the HSK arbor is removed from the spindle. The transfer rod is selected and longitudinally aligned and connected to the internal threads on the grip-housing. The guide piece is then selected and longitudinally aligned over the grip-housing and the distal end of the transfer rod that extends from the grip-housing. In the preferred embodiment, the force exerting means is an upper frame member, a clevis, and a pressure jack. During assembly, the shank of the upper frame member is inserted into the bore formed on the guide piece and threadingly connected to the proximal end of the transfer rod. The pressure jack is then inserted inside the upper frame member and the clevis is positioned over the upper frame member""s lower horizontal member. As a pulling force is applied to the transfer rod via the drawbar assembly, the upper frame member is then pulled towards the clevis thereby applying pressure to the pressure jack. The interior shape of the front cavity formed inside the guide piece is identical to the geometry of the HSK arbor except that the lower conical section is slightly smaller in diameter which allows the grip-housing to be pulled towards the spindle when the drawbar assembly is activated. Before the lower conical section of the grip-housing contacts the surfaces of the front cavity, the gauge attached to the pressure jack measures the tension force to determine if the drawbar assembly holding force on the grip housing is within acceptable operating specifications.